(1) Field of the Invention
The present invention relates to the art of continuous molten metal casting and more specifically to an inner nozzle with specific means or elements for fixing it to a tube exchange device in a metal casting facility.
(2) Description of the Related Art
In a casting facility, the molten metal is generally contained in a metallurgical vessel, for example a tundish, before being transferred to another container, for example into a casting mould. The metal is transferred from the vessel to the container via a nozzle system provided in the base of the metallurgical vessel, comprising an inner nozzle located at least partly in the metallurgical vessel and coming into tight contact with a sliding transfer plate (or casting plate) located below and outside of the metallurgical vessel and brought into registry with the inner nozzle via a device for holding and replacing plates, mounted under the metallurgical vessel. This sliding plate may be a calibrated plate, a casting tube or a saggar comprising two or more plates. Since all these types of plates are part of a nozzle comprising a plate connected to a tubular section of varying lengths depending on the applications and to distinguish them from valve gates used, e.g., in a ladle, they will be referred to herein as “sliding nozzle”, “pouring nozzle”, “exchangeable pouring nozzle” or combinations thereof. The pouring nozzle can be used to transfer the molten metal in the form either of a free flow with a short tube, or of a guided flow with a longer, partly submerged casting tube.
An example of a tube exchange device for a casting facility is described in the document EP1289696. To provide tight contact between the inner nozzle and the sliding nozzle, the tube exchange device for holding and replacing pouring nozzles comprises clamping means, intended to clamp down the inner nozzle against the frame of the device, and pressing means, intended to press on the plate of the pouring nozzle, particularly upwards, so as to press the plate against the inner nozzle, and to thus obtain a tight contact.
As described above, the inner nozzle is a fixed element during casting. Therefore, the service life thereof should be at least as long the one of the metallurgical vessel. The pouring nozzle, on the other hand, may be replaced during casting by means of the tube exchange device.
EP1454687 discloses a collector nozzle to be connected to a sliding gate of a gate valve located at the bottom of a ladle, used for pouring molten metal into a tundish. Like the inner nozzle of a tundish, the collector nozzle disclosed in EP1454687 comprises a refractory core comprising a tubular portion and a plate, most of the external surface of the collector nozzle being clad with a metal casing. This is where the similarities between the two types of nozzles end. Indeed, unlike an inner nozzle, subject of the present invention, the collector nozzle of a ladle does not undergo any frictional stresses during use, as it is fixedly attached to a slide gate plate of a slide gate valve. Furthermore, the collector nozzle is hanging at the bottom of the ladle, whilst the inner nozzle rests on the upper portion of the frame of a tube exchange device. The clamping means used for the two types of nozzle consequently differ substantially from one another. In the collector nozzle disclosed in EP1454687, the nozzle is introduced into a first metal cylinder comprising a flange which engages as a bayonet with a second metal cylinder fixed with screws to the lower portion of a slide plate of a slide gate valve. None of the first and second metal cylinders are part of the collector nozzle, and are rather the clamping means used to fix the collector nozzle to the lower surface of the slide gate plate. This clamping solution of a nozzle to a metallurgical vessel is not suitable for clamping an inner nozzle to the upper portion of the frame of a tube exchange device.
The inner nozzle and the plate of the pouring nozzle each comprise, at least in part, a refractory material. One problem lies in that the forces applied by the clamping or pressing means tend to apply stress concentrations on the refractory material. These stress concentrations may damage the brittle refractory material, and form cracks or lead to crumbling.
The present invention aims at providing an inner nozzle in which material quality and integrity will be maintained during the whole service lives of both nozzle and metallurgical vessel.